Vitamin C is a powerful antioxidant that may help neutralize the damaging effects of free radicals, the unstable chemicals that are a result of air pollution, smoking,stress and sunlight.
Studies suggest that Vitamin C has the potential to stimulate the growth of collagen that is important in maintaining healthy skin elasticity and texture.
Vitamin C in the form of L-Ascorbic acid is the chemical form of ascorbic acid that is reported to be most effectively utilized by the body.
Treatment of photo-aged skin and resultant wrinkles and other sequelae with ascorbic acid and related derivatives has been discussed in the prior art. Among the most common treatment regimen is a topical application of ascorbic acid to affected areas of the skin in lotions, creams and other delivery vehicles, such as discussed in U.S. Pat. No. 5,140,043 of Darr et al for stable ascorbic acid compositions.
In Darr '043, it is noted that L-ascorbic acid prevents ultraviolet (UV) damage to the skin. In the discussion of the background art therein, Darr '043 states that ascorbic acid, also commonly known as Vitamin C, acts as an anti-oxidant to counteract the skin damaging effects of superoxide and hydroxyl radicals, which have been known to cause a wide variety of damaged skin conditions ranging from transitory sunburn to permanent wrinkles from photo-aged skin. According to Darr '043, these radicals destroy lipid membranes, break down DNA and inactivate beneficial enzymes which promote healthy skin conditions, citing Cerutti, D. et al, eds. Oxy-radicals in Molecular Biology and Pathology, (Alan Liss, publisher, New York, N.Y. 1988), Hayaishi, O, et al, eds., Biological Role of Reactive Oxygen Species in Skin, (Elsevier Press, New York, N.Y. 1987), Johnson, Jr., J. E. et al, eds., Free Radicals, Aging and Degenerative Diseases, (Alan Liss publisher, New York, N.Y. 1986), Halliwell, B. et al, eds, Free Radicals in Biology and Medicine, (Clarendon Press, Oxford, U.K. 1985), and Sied, H., ed., Oxidative Stress, (Academic Press, 1985), among other cited publications therein.
Free radicals from ultraviolet light (UV) are known to increase with air pollution in areas of concentrated populations, thereby magnifying the problem. The free radicals are destructive in that the free radicals hydrolyse elastin fibers in the skin and desynthesize collagen in the lower dermal layers of the skin, thereby causing skin wrinkles and other damaging skin conditions.
In contrast, it has also been known that ascorbic acid is effective in counteracting the effects of free radicals upon the skin. Ascorbic acid absorbs ultraviolet (UV) radiation and at the same time stimulates collagen production.
However, ascorbic acid, such as Vitamin C, is difficult to stabilize for any significant period of time in pharmaceutical vehicles for topical delivery to the skin. Ascorbic acid loses potency and discolors easily in most delivery vehicles. Furthermore, ascorbic acid hydrolyzes when exposed to water.
The term "stable" is defined as a characteristic wherein a composition retains potency for the duration of a predetermined expiration period, as defined by generally accepted pharmaceutical protocols, such as "GMP", or "good manufacturing practices" as promulgated by various trade conventions, such as for example, the United States Pharmacoepia (USP) convention.
For example, for a topically applied skin care formulation, the expected duration of a predetermined expiration period should be at least eight months before the formulation loses significant potency.
In contrast, Darr '043 only tested the product described therein for twelve weeks.
Moreover, as noted in Darr '043, ascorbic acid washes off easily when exposed to water, so that topical application at a sun-lit beach is generally futile, since swimming washes away the topically applied ascorbic acid.
Furthermore, in the past, ascorbic acid has been administered in high dosages to the skin, and has to be made every day because of its instability, thus increasing cost of its use.
Darr '043 discloses a method of stabilizing ascorbic acid in a water based delivery system with an ascorbic acid to water/carrier ratio of at least 1:1, preferably 2:1 to 10:1.
The ascorbic acid and water mix described in Darr '043 includes both water and a carrier, such as alkylene glycols, or alkylene glycols in combination with one or more derivatives of hydroxyalkyl-cellulose. However, the minimum amount of water in the product disclosed in Darr '043 is fifty (50) percent, since Darr '043 teaches at least a 1:1 ratio of water to carrier, preferably greater than fifty (50) percent, such as sixty seven (67) percent water in a 2:1 ratio, up to ninety two (91) percent water in a 10:1 water/carrier ratio.
In general, the carrier is described as being compatible with water, preferably distilled or deionized water without contaminants, which further de-stabilize ascorbic acid.
However, the disadvantage of the delivery vehicle in Darr '043 is that it is water-based, and therefore the ascorbic acid is still inherently unstable.
For example, while FIG. 1 of Darr '043 shows small drops in potency of L-ascorbic acid of less than 10 percent over seven weeks at room temperature for L-ascorbic concentrations of three (3), five (5) and ten (10) percent respectively, FIG. 1 shows a drop in potency of approximately 30 percent over seven weeks, from 100 percent to 70 percent, of L-ascorbic acid in a concentration of one (1) percent.
Moreover, FIG. 2 of Darr '043 shows all four samples of L-ascorbic acid having lost potency of at least ten (10) percent over eight (8) weeks at room temperature, when stored under controlled conditions in the dark.
Furthermore, while the testing in Darr '043 was conducted from between seven (7) and twelve (12) weeks duration, any viable over the counter consumer product requires in excess of twelve weeks from manufacture through distribution points to final retail sale, and must still afford the consumer a reasonable time to consume the contents of the product. Therefore, a loss in potency of the magintude as shown in Darr '043 in such a short time span, raises serious questions as to the usefulness of the stability data obtained in predicted the potency of L-ascorbic acid at the time the consumer is able to use the product.
Therefore, the response of the ascorbic acid in the epidermis and dermis of the skin is not very effective, because of the presence of substantial amounts of water, which contribute to destabilization of the ascorbic acid.
The present invention utilizes a single phase carrier, as opposed to an emulsion, as the anhydrous base. Emulsions are more complicated compositions than single phase carriers, and are discussed in Remington, Remington's Pharmaceutical Sciences, Mack Publishing Co., Easton, Pa. 1975, pp 327-331, Sagarin, Cosmetics Science and Technology. Interscience Publishers, Inc., New York, N.Y. 1957, pp. 998-1003, Wilkinson et al, Harry's Cosmetology, Chemical Publishing Co., New York, N.Y. pp 729-741.
Such an emulsion for ascorbic acid is shown in U.S. Pat. No. 5,587,149 of Punto et al for a topical emulsion for ascorbic acid. Punto '149 describes two phase emulsions for stabilizing water-soluble active ingredients, such as ascorbic acid. For example, Punto '149 describes a two phase polyethylene glycol-in-oil emulsion. In Punto '149, the glycols are first dissolved in a water phase in a first phase. Secondly, an oil, such as silicone #1, is introduced in a second oil phase. Dispersion agents are then added to create an emulsion between the components of the first water phase and the second oil phase. However, Punto '149 does not describe the making of an anyhydrous base in a single phase carrier, as opposed to a two phase emulsion.